Characterization of the Cytosol Androgen Receptor of the Human Prostate*

Abstract

Direct measurement of the binding of endogenous androgens to the androgen receptor of human tissues has not been possible because of contamination of tissue with traces of plasma proteins, such as testosterone-binding globulin (TeBG), that contain more androgen-binding capacity than does the receptor itself. Molybdate is known to stabilize the 8-9S forms of other steroid hormone receptors. We took advantage of this phenomenon to characterize the androgen receptor of hyperplastic prostates removed at surgery, using sucrose density gradient centrifugation in a vertical rotor. In 10 mM sodium molybdate, the androgen receptor sediments as a distinct 9.2 +/- 0.5S moiety, easily separable from TeBG. Unlike TeBG, the 9S receptor is not removed by absorption with Concanavalin A. [3H]Dihydrotestosterone (3H-labeled 17 beta-hydroxy-5-alpha-androstan-3-one) binding to the 9S receptor is not removed by absorption with Concanavalin A. [3H]Dihydrotestosterone (3H-labeled 17 beta-hydroxy-5 alpha-androstan-3-one) binding to the 9S receptor is not competed for by excess triamcinolone acetonide (9 alpha-fluoro-11 beta, 16 alpha, 17 alpha, 21-tetrahydroxypregna-1,4-diene-3,20-dione cyclic 16,17-acetonide) or promegestone (17,21-dimethyl-19-non-pregna-4,9-diene-3,-20-dione), which are known to bind to the progestin receptor. In contrast, [3H]methyltrienolone (3H-labeled 17 beta-hydroxy-17 alpha-methyl-estra-4,9,11-trien-3-one) binds to both androgen and progestin receptors, and consequently, the binding of this ligand to the androgen receptor was assessed in the presence of a 500-fold excess of triamcinolone acetonide. The amounts of 9S binding (7.8 and 5.8 fmol/mg protein) are similar for dihydrotestosterone and methyltrienolone. The amount of 9S binding of testosterone to the receptor was also similar to that of dihydrotestosterone, but the affinity of testosterone for the 9S receptor was only a fifth or less of that for dihydrotestosterone. The observation that testosterone binds less avidly than dihydrotestosterone to the receptor may explain the role of dihydrotestosterone formation in androgen physiology.

Changes in amount and intracellular distribution of androgen receptor in human foreskin as a function of age.

“…Under these conditions, it made no difference whether the samples were incubated for 1 h (shorter periods were not examined) or 24 h before applying them to density gradients (results not shown). As previously reported for human prostate (16) and foreskin (1 1-13), freezing the tissue in liquid nitrogen for as long as 3 d had no effect on the receptor levels (Table I). Methyltrienolone was used as the binding ligand because it is not metabolized at a significant rate by either cytosol or nuclear extracts (results not shown) and because it binds weakly to testosterone-binding globulin of plasma.…”

Chronic administration of androgens with actions at estrogen receptor beta have anti-anxiety and cognitive-enhancing effects in male rats

“…In some, but not all studies, a correlation has been found between T replacement therapy, and an increased risk of prostate cancer in men (Marks et al 2006). Development of prostate cancer often results from abnormal activation of ARs, which can be precipitated by circulating androgen levels (Guerini et al 2005), in particular DHT because of its greater affinity for ARs than T, especially in the prostate (Grino et al 1990;Kaufman and Pinsky 1983;Wilbert et al 1983). As such, therapeutics often prescribed for some types of prostate cancer include finasteride, to prevent binding of DHT to those abnormal ARs (Rittmaster 2008).…”

Polymorphism of the SRD5A2 gene and the risk of prostate cancer

“…It has been hypothesized that variation in the genes involved in androgen biosynthesis and metabolism may be risk factors for prostate cancer (12). One of these genes is steroid-5-α-reductase, which irreversibly catalyzes the conversion of testosterone to its more active and most potent androgen DHT (13,14).…”

“…Subsequent to catalysis of this enzyme, the binding affinity of DHT to an androgen receptor is five times higher compared with that of testosterone (13). It has been demonstrated that young Japanese males have a lower steroid-5-α-reductase activity compared with young Caucasian-American and African-American males (15), and the DHT:testosterone ratio was highest in African-Americans, intermediate in Caucasians and lowest in Asian-Americans, corresponding to the respective risk of developing prostate cancer in these groups (16,17).…”